I want to make a game that has the best performance on every resolution on 16:9
I mean display quality doesn't change on different resolutions
I have to make it 720p or 1080p?
what res are you talking about ?
What kind of gfx? Pixel art or hi-res? What's the game's native resolution?
There are methods to get games to run faster on high device resolutions (desktop resolution on computers) but whether they're suitable depends on what kind of graphics and what kind of resolution you use for your game.
I want just to start making my game but I dont know make it on which resolution
make my game 720p or 1080p?
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that depends on the Platform you want to use
I want to make it for PC
1080p is good for that
If I make it on 1080p, someone that has to play it on lower resolution doesnt have any problem?
https://www.scirra.com/tutorials/73/supporting-multiple-screen-sizes/page-1here is a Tutorial